A, w-dicarboxylic acids

XIV). This reaction also gives good results with unsaturated a,w-dicarboxylic acids having odd carbon chains (210).5> 136, 137 The resulting methine color salts (211) are of interest on account of their... 

As minor oxidation products, C1-C3 monocarboxylic acids and C4 a,w-dicarboxylic acid were obtained (1-2% of the initial humin carbon). The humin was then hydrolyzed by 6N HCl at 110°C for 24 hours, and the unhydrolyzable part of humin was oxidized. Interestingly, degradation products of the unhydrolyzable part of humin were almost the same as those of the original humin although 30-49% (by weight) of the original humin was released into solution on HCl hydrolysis. 

Oxidative degradation was conducted for fulvic acid obtained after dialysis (Ishiwatari and Machihara, 1983). As shown in Figure 3, oxalic acid, n-C4 and -Cg a,w-dicarboxylic acids, and benzoic acid were major degradation products for fulvic acid. Oxalic acid accounted for 44% of a,w-dicarboxyIic acid in the degradation products and was considered to have been derived predominantly from carbohydrates and amino compounds present in the fulvic acid. 

The distribution pattern of a,w-dicarboxylic acids for lipids resembled those for humic acid and humin (Fig. 3). This fact clearly indicates the common origin for the polymethylene chains in lipids, humic acid, and humin, which means that phytoplankton-derived lipids actively took part in the formation of humic acid and humin. The relative abundance of polymeth-ylene chains in lipids and humic substances was estimated on the assumption that the yield of production of aliphatic acids from polymethylene chains by alkaline permanganate oxidation was the same for these organic fractions. The following estimations resulted 42% (% of the total amount of polymethylene chains in the sediment) for humin, 38% for lipids, 19% for humic acid, and 1% for fulvic acid. 

Suberin, suberic acid. Suberin (Latin suber=cork) in plants forms the lipophilic protective layer on the outer dermal tissue (cork) of trunks and branches as well as roots and other underground plant parts (see cutin). S. is also formed in plant tissues during wound healing. S. is a mixture of polyesters, the main components are a,w-dicarboxylic acids, e.g., docosane-dioic acid (see Japan wax) and tetracosanedioic acid (C24H46O4, Mr 398.63, mp. 127.1 °C), tt>- hydroxy fatty acids, fatty acids, and fatty alcohols as well as phenolic compounds. 

Various commercially available Hpases have been shown active for the polymerization of sebacic acid and 1,8-octanediol. In the polymerization of a, dicarboxylic acid and glycol, the polymerization behavior depended heavily on the aliphatic chain length of the monomers. Typically, the polymer was obtained in good yields from 1,10-decanediol, but no polymer formation was observed with 1,6-hexanediol. This suggested that a combination of monomers with appropriate hydrophobidty would be favored for an efficient enzymatic polymerization. 

Methanolysis under mild conditions has been studied mainly for structural elucidation purposes [7, 51, 60]. However, such conditions can also be considered for the preferential isolation of specific groups of components, such as the alkanoic and a,w-dicarboxylic acids generally involved in more labile structures [7,51,60]. Finally, methanolysis in the presence of calcium oxide was shown to yield oligomers [39, 40, 48-50, 59, 67], which, apart from their interest for structural elucidation, might also be considered as macromonomers for other applications. However, these mild methanolysis conditions are marred by an important drawback in terms of their use as sources of monomers/macromonomers for polymer synthesis, because they generally result in quite low yields. 

As in the case of total suberin contents in its natural precursors, the monomer composition and abundance are also highly variable, but in general the most abundant families of compounds are m-hydroxyfatty acids, followed by a,w-dicarboxylic acids and by smaller amounts of fatty acids, aliphatic alcohols and aromatic compounds. 

In the case of birch outer bark suberin, only the C(18 l) and C(22 0) homologues were found in considerable amounts, whereas in the case of cork suberin, the 9,10-epoxy and the corresponding 9,10-dihydroxy CIS a,w-dicarboxylic acids are dominant. 

Two new long-chain acyl amino acids, sagittamides A and B, were isolated from an unidentified didemnid collected from Arrow Island, Pohnpei. These compounds possess a long-chain C26 a,w-dicarboxylic acid, each of them acylated by a different a-amino add (Lievens and Molinski, 2005). The relative stereochemistry of the hexaacetoxy moiety of sagittamide A was determined by different techniques of NMR (Lievens and Molinski, 2006 Seike, Ghosh, and Kishi, 2006 Sdiuetz et al, 2007). 

---